1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device such as a thin semiconductor device having a plated heat sink (PHS) metal layer for dissipating the heat from a back surface of the device.
2. Description of the Related Art
Generally, a semiconductor wafer is constructed by a plurality of pellet (chip) portions and pellet dividing portions therebetween. The pellet dividing portions are also called etching cut portions.
As semiconductor devices have been developed, the thickness of the semiconductor devices has been reduced to suppress the increase in temperature of the semiconductor devices. Also, in order to cool the semiconductor devices, PHS metal layers are formed on the back surface of the semiconductor devices.
In a prior art method for manufacturing a thin semiconductor device having a PHS metal layer on the back surface thereof, the front surface of a semiconductor wafer is adhered to a transparent supporting plate by an adhesive element. Then, the back surface of the semiconductor wafer is polished and made thinner. Then, the back surface of the semiconductor wafer is etched, so that via holes and etching cut portions are formed within the semiconductor wafer. In this case, a plurality of pellets (chips) are surrounded by the pellet cut portions. Then, a plating path metal layer is deposited on the entire surface by an evaporating process. Then, a photoresist pattern layer is formed in the etching cut portion of the semiconductor wafer on the plating path metal layer. Then, a PHS metal layer is electroplated on the plating path layer by applying a negative voltage to the plating path metal layer and a positive voltage to an electrolytic bath (not shown). Finally, the pellets are separated from each other by performing a dicing process or the like upon the supporting plate in the etching cut portions. In this state, each of the pellets is associated with each piece of the supporting plate. Then, the adhesive element Is removed by using organic solvent or the like, so that each of the pellets is separated from each piece of the supporting plate. Thus, the pellets each having a plated heat sink and via holes are completed. This will be explained later in detail.
In the above-mentioned prior art method, when the pellets are separated from the supporting plate, contamination may be introduced Into the pellets by the residual adhesive elements, or marks or cracks may be generated in the pellets. This decreases the manufacturing yield.
Also, the supporting plate adhering step and the supporting plate separating step decrease the productivity.
Further, when the semiconductor wafer is adhered to the supporting plate, cracks are easily created in the semiconductor wafer, since the semiconductor wafer is generally warped more or less.
Additionally, since the photoresist pattern layer is formed on the back surface of the warped semiconductor wafer, the alignment accuracy of the via holes is deteriorated. As a result, it is impossible to form more-fined via holes